1. Field of the Invention
The present invention relates to a fixing apparatus capable of fixing a toner image on a recording material. The fixing apparatus can be used for an image forming apparatus, such as a copying machine, a printer, a facsimile machine, and a multifunction peripheral (MFP) including a plurality of such machines. The image forming apparatus forms the toner image to the recording material with image formation processing, e.g., an electrophotographic process, an electrostatic recording process, or a magnetic recording process.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2007-240622 discusses a fixing apparatus using a fixing belt for high-speed image formation. The fixing apparatus includes the fixing belt and a pressure belt facing each other. In a fixing nip between the fixing belt and the pressure belt, fixing processing is performed while the fixing nip nips and conveys a recording material.
The fixing apparatus further includes a pressure pad and a pressure roller inside the pressure belt to form the fixing nip between the pressure belt and the fixing belt. A sliding contact sheet covers the pressure pad to improve slidability to the pressure belt.
When forming the fixing nip long in a recording material conveying direction, if there is an area with large reduction in pressure between the pressure pad and the pressure roller, water vapor generated from the recording material is not suppressed in the fixing processing. That may cause uneven gloss. Therefore, it is required to prevent the occurrence of a pressure-reduction portion.
Longitudinal end portions of the pressure roller are configured to press against the fixing belt. Therefore, it is desirable to set a shape of the pressure roller that an external diameter of a longitudinal central portion is larger than that of the longitudinal end portions, that is, a positive crown shape.
When using the positive crown shaped pressure roller, in a longitudinal direction of the pressure roller, the distance between a leading edge of the sliding contact sheet and the pressure roller is longer at the end portions than that in the central portion. The pressure tends to be reduced at the end portions. As a result, that may cause the uneven gloss due to the reduction in pressure at the end portions.
In consideration of the reduction in pressure at the end portions, the distance between the leading edge of the sliding contact sheet and the pressure roller may be shorter than that compared with the conventional art. However, with such countermeasure, the leading edge of the sliding contact sheet may be pinched between the fixing belt and the pressure roller. Then, in the longitudinal direction of the pressure roller, the pressure at the central portion is rather reduced. Thus, that is not the countermeasure.